Electrical protective apparatus



March 27, 1951 P. P. KOLISS ELECTRICAL PROTECTIVE APPARATUS Filed Dec. 11, 1947 5 RS n 0 N TL R N0 0 w w WP Q A R W Ow ([1 V B Patented Mar. 27, 1951 UNITED STATES PATENT OFFICE ELECTRICAL PROTECTIVE APPARATUS Peter P. Koliss, West Orange, N. J., assignor to Bell Telephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application December 11, 1947, Serial No. 791,007

Claims. 1

This invention relates to electrical protective apparatus and particularly to a central oifice protector of the combined type.

In accordance with modern telephone engineering practice it is usual to provide, at the central office or other switching point, protectors for each incoming line of the so-called combined type. That is, these protectors combine protection against excessive voltages resulting, for example, from lightning, with protection against so-called sneak currents, that is, currents which are not strong enough to do any damage if they flow only for a short time but which might cause enough heating to char insulation and to do other damage if they were to persist. The sneak currents are produced by voltages of a relatively low magnitude as compared to the excessive voltages first mentioned and usually result from accidental contact between the telephone line and adjacent power lines.

The first type of protection is usually provided by so-called open gap protectors commonly in the form of two carbon electrodes with a small gap between, one of which electrodes is connected to ground and the other of which is connected to the incoming line. Should a high voltage be impressed on the line it will bridge across the gap to ground thereby being diverted from the sensitive equipment associated with the line.

The second type of protection is commonly provided by a device usually referred to as a heat coil. The heat coil consists essentially of a coil of fine wire wound on a metal tube inside of which a pin is held in position by solder. Should sneak currents be impressed on the line and persist, sufficient heat will be generated to melt the solder and release the pin. A spring is usually provided which will then push the released pin forward to contact a ground plate whereby to ground the line and protect the sensitive line equipment.

For obvious reasons of efiicient maintenance it is usual to group the functional protective means of each line or each pair of lines, i. e., open gap protectors and heat coils, on a common supporting means hence the term combined type protector. As heretofore designed, these assemblies usually include long cantilever springs of such dimensions as to accommodate the functional elements and to provide the required spring pressures for their operation. The springs extend through a clamped pile-up and serve as soldering terminals for the line connections. Patent 1,057,126, issued March 25, 1913, to Mr. A. F. Dixon, illustrates the essential features of such a combined type protector. While this and other previously used types of protector assemblies have rendered efficient and generally satisfactory service over a period of years, it has been recognized that certain undesirable features do arise in connection with their use. The type of combined protector contemplated by the present invention eliminates the undesirable features of previous designs.

Similar protective equipment is also commonly provided on electrical lines other than telephone lines, for example, telegraph lines, lines for the transmission of alarm signals and the like.

It is an object of the present invention to afford adequate protection to electrical lines in a more efiicient and economical manner than has been done heretofore.

A further and more specific object of the invention is the reduction of the likelihod of circuit noise occurring in the line due to the association of the protective means with the line.

Still another specific object of the invention is the reduction of the likelihood of interference with adjacent line equipment when a given protector assembly is being tested or replaced.

A still further specific object of the invention is the reduction of personnel hazard from the standpoint of accidental contact with voltages by attendants when servicing or replacing the protector elements.

According to a feature of the present invention the functional protective elements of each line are enclosed in individual recesses in a housing. This is effective in protecting the elements against dirt accumulation as well as atmospheric corrosion whereby the possibility of circuit noise being caused by such effects is materially reduced. Further, interference with the protective elements of adjacent lines when a given protector assembly is being worked on is effectively prevented.

In accordance with a further feature of the invention a line is automatically connected to ground immediately upon the removal from the housing of the protective elements provided for that line.

In accordance with a still further feature of the invention a plate, which is likely to be contacted by the attendants when servicing or replacing protector elements, is maintained completely at ground potential at all times whereby to remove the hazard of accidental contact with voltages while working on the protectors.

In accordance with a specific embodiment of the invention, a molded plastic housing is provided for accommodation of a given number (say 200) of protectors. The housing is provided with a face plate of suitable conductive material; this plate is connected to ground whereby to provide the common ground connection for all of the protectors. The connection of the face plate to ground may-ybe .by any suitable means; for example contact-with a grounded portion of the mounting frame may be utilized or a separate conductor to a ground terminal may be provided. individual recesses each of which" accommodates the assembled functional protective elements. of

forminga terminal to which the corresponding a given line. The face plate is provided .with a plurality of spaced apertures each of whiclr'is in registry with a respective one of;.the housingrecesses.

The functional elements for a particular line' include the protector blockassembly comprising the-springs referredto. are helical withback- The housing is provided,with,spaced,.,..,,

4 being closed by the bayonet caps which form a part of the protector assembly.

Referring for the moment to Figs. 2 and 3, the functional protective elements associated with a given telephone line are illustrated. These elements comprise; first, the protector block assembly, including two space-d, cylindrical carbon electrode blocks l3 and hi and protectoriblock spring l5 and washer I5; and, second, theheat coil assembly including heat coil 2! and heat coil spring 22. Protector block spring i5 is providedwith a backwardly extending arm 23 forming a terminal'to which the incoming telephone :1. line is connected; ,heatcoil spring 22 is provided with a similar backwardly extending arm 24 central office. line is connected. The helical springs I5 and 22, when compressed as in Fig. 2,

exert =a'pressure of the orders of 3 and 4 pounds wardlyextending-arms for connection of the incoming .telephoneline and the central office line or otherzterminating line respectively.

The bayonet caps referred to act as closure membersifor the respective apertures in'the face.

plateand are readilyiremovableto permit access to theprotectors .from'the front of the housing. soldered. connectionsare made at the rear of the housing while inspection, testing, etc., is done? from the front of the :housing. I

Full understandingof the nature of the arrangement contemplated by the present invention and the method of its operation; as well as appreciation of the a various desirable features thereof, maybe gained from consideration of the following detailedidescription and the annexed drawings. in which:

Figfilis a frontelevation view of a-hou'sing for mounting anumberof combined protectors;-

Fig. ;2 is'a sectional viewtaken on line 22 of Fig. 1 showing details of an assembly of the functional units associated with one line Fig. 3 is .an.exploded-v-iew'in partial section Referring now -to the drawingsgthere is shown in Fig.1 a housing such as-may be provided in a telephone central office. for mountinga number, say 200, of combined protectors.

with a .metalfaceplate I2. .The face plateis connected to-ground by-suitablemeans; as poin ed out above -personnelhazardfrom the standpoint of contact with voltages is removed by this expedient wherebythe face plate is -maintained completely at ground potential.-

The plastic block is provided with a-number of spaced recesses in each of whichis positioned the functional protective elements for a given tele- The housing, may comprisea molded-plastic block I I providedphone line. "The faceplate i2 is providedwith apertures registering respectively with the recesses'in the block wthese apertures-normally respectively against washer i6 and. heat coil 2|.

When :the elementscare in assembled position (Fig. 2) bayonet cap'25- actsas a closure member for the aperture in faceplate-I2 and also as a housing for carbon electrode bloclc it and as an end stops for the entire assembly. The second carbonvblock i4 is positioned within metallic housingf'fi; ceramic spacer ring 2? is positioned between-the face of carbon block i3 and the baseof: housing member 26 and is effective to maintaina gap'of the orderof 3 mils between the adjacent faces of arrestor-blocks i3 and M. Heat'coil 2| comprises acylindrical housing l! of suitable insulating-material with a metallic end cap 42. End cap Hand metalrpin 43 areanchored to housing 4!, pin 43 being insu-- i A metallic lated ,frorrv cap 52;byinsulatorilil. sleeveor tube fi i'su-rrounds pin 43 and a winding 45 offine wire-is placed'around-the sleeve, one

end 'of-the' winding beingconn'ected to sleeve,

for example by soldering; and the'other-end being connected-to end cap 42 the extremeend portion of the-winding beingextended'as lead'wire 46 for that'purpose. The space between-pin 43 and the insideofsleeve 44*.isnormally filled :with' low melting-point solder, the solder, when in solidified state being'eifective to normally hold the parts 1 of the heat; coil inithe position .ofFig. 2 against the force-of compressedspringZfl When in the assembledposition'of Fig. 2, the projecting'end of pinis positioned in aperture. of carbon It will be:.apparent that the various elements of the protector. assembly may be easily reached for examinationand .testingifrorn the front of the housing. simply: byxremoving bayonet cap 25 and, as set forth'subsequently, all elements, ex-

cept springs '23 andtid, maybere'adily' removed from the front of .thehousing,.the line being immediatelygrounded thereupon. As shown, spring. arms: 23' and 2d are provided with projecting lugs which seat in indentations in the rear of the housingcwhereby to hold the springs in proper malincoming telephone currents pass through arm 23; spring-idw asher i6, baseof housing 26 andthroug'h the conductive portions of-heatcoil H 2 I, i';t'e., 5 sleeve "44, winding fii' lead wire-- -46 and cap 42 to spring 22 and thence over arm 24 to the central office line. These normal currents are of insufficient voltage to traverse the gap between carbon blocks I3 and I4 to ground.

Should dangerously high voltages appear on the line, however, as a result, for example, of lightning discharges, such currents will easily bridge the gap between the carbon blocks and, consequently, instead of taking the longer path through the heat coil and associated parts, will pass directly to carbon block I3 and through bayonet cap 25 to ground on face plate I2. [It will be noticed that the arrangement of housing 2B"is such that a shallow indentation prevails between'the edge of block I4 and spacer 21. This is effective to prevent a build-up of carbon'particles between the adjacent faces of the carbon blocks in the event of repeated arcing between'the two blocks. I

As set forth above, so-called sneak currents sometimes appear on a telephone line which, if persistent for a sufficient length of time, may cause charring of insulation and other damaging effects. With the use of the present arrangement, if such currents prevail they will cause sufiicient heat in heat coil winding 45 when passing therethrough to melt the low melting-point solder which normally holds the parts of the heat coil in retracted position. Upon melting of the solder and release of pin 43 from its position in sleeve 44, theencrgy of compressed spring 22 will project housing III and pin 43 carried thereby forward to the position shown in Fig. wherein the tip of the pin projects all the way through aperture 41 of carbon block I4 to engage carbon block I3 whereby to connect the incoming currents directly to ground on face plate l2 and prevent damage to the delicate apparatus associated with the central office line.

' 'In accordance with a special feature of the present invention, should the protective elements of a given line be temporarily removed, as'is often done for purposes of inspection or repair, the line is immediately grounded. The manner in'which this is accomplished will be apparent from Fig. 5. As the elements are removed through the aperture in face plate I2, spring I5 will force washer 8 to follow until it contacts the grounded' faceiplate thereby connecting the incoming line to ground. a (The diameter of washer I6 is such that it will not pass through the aperture in face plate I2.)' The biased lug provided on arm 23 and seated in the indentation provided in the rear of the housing serves to hold spring I5 in position.

}, The; particular arrangement of the bayonet caps with respect to the. apertures in face plate I2 is shown particularlyin-Fig. 6. When cap 25 (which is illustrative of all of the bayonet caps) is to be inserted in the associated aperture in face plate I2, it (cap 25) is sopositioned that the lugs carried thereby, i. e., lugs 'II, I2 and I3, are aligned with respective slots I4, I5 and 16 provided in face plate I2 whereupon the cap 'may be inserted and rotated clockwise to the position shown in Fig. 6. It will be observed that further clockwise rotation is prevented by engagement of lug II and stop I1 which is provided onthe inner face of plate I2; in this position lugs II, 12 and I3 are automatically aligned with the corresponding slots 14, I5 and IS in the face plate whereby to permit removal of the cap.

-It will be apparent from the preceding description, and by again referring now to Fig. 1, that the arrangement is such that a considerable number of desirable features, not found in the arrangements previously known, are provided. Location of the protector assembly of each line in a separate individual recess in the housing results in various advantages. For example, the contact elements and other portions of the assembly are shielded against dirt accumulation and atmospheric corrosion whereby to materially reduce the possibility of circuit noise occurring from such effects. Enclosure of each protector assembly in a separate housing substantially eliminates the chance of interference with adjacent assemblies When a given unit is being serviced. Projection of springs into the aisle is eliminated together with the chance of snagging and the necessity of spring repair and displacement. The soldering operations may be conveniently performed at the rear of the housing while the bayonet cap closure members at the front of the housing may be readily removed to permit inspe-ction and servicing of the units from the front of the housing; test fixtures may be conveniently used from the front of the housing upon removal of the bayonet caps.

The arrangement lends itself to convenient marking or identification of special lines as used, for example, in broadcasting networks. Such identification may be by use of colored plastic caps placed over the respective bayonet caps or, as shown in Fig. 1, by use of distinctive markings placed on certain of the bayonet caps themselves as shown on caps 5|, 52 and 53. The colored plastic caps, when used, may serve, in addition to their identification function, as means for locking the bayonet cap in position whereby to provide additional assurance against accidental disturbance of the special lines.

A bayonet cap may be removed by a simple partial turn in the usual manner. The ease with which the protector assemblies may be inserted in the associated recess in the housing and the simple, accurate and eificient manner in which they are held in assembled position after closure of the associated bayonet cap will be apparent from the drawings. As shown, the springs, after insertion, are held in position in the recess in a simple manner by provision of the biased lugs on the projecting arms. The fact that the spring arrangement is such that the line connections are made directly thereto is a desirable one as it cable is terminated; a high insulation resistance forv the incoming lines is thus assured as the wires are not exposed to atmospheric conditions at any point in the central office. The arrangement may be utilized to advantage at switching points along the line other than at a central office in which event the terminal corresponding a qcc szc torterminalz l ingtherabove description would be connected to. arrrappropriate terminatingiiine,

W hile certain specific embodiments ofzthe invention -have :been'i'selected for detailed :dESOIiP-r tio'n; the invention isinot, :oticourse;limited in its application to such:-embodimentsic::Fo'rexample; the invention maybe'iappiied to-electricaltrans mission:- :line's oth'er than telephone? lines." 1 @The embodiments .descriibe'd should betaken 'as illustrative" ofmthe invention- :and' "not as restrictive thereof.

What' is claimed is:

1: An electrical protector-comprising a housing of insulating "material; a face plate of conductive material for" said-housing, said=housing having a plurality" of recesses ther'ei'n', .a protector assemblypositione'd ineach of the recesses; said protector assembly including a heat fcoil and a spaced gap protector; said spac'ed gap protector comprising"two-cylindrical blocks and-means for holding -said blocks in spaced relationship, said blocks andsaid heat coil-being alig ne'd'horizom tally in th'eirrespective' recess along a'-*co'rn-rnon horizontal axis, a first and a second: helical spring for exerting -pressure oil-elements of said pmtector assembly; whereby tonori'nallyv maintain the elements of'the 'a'sser'nbly in compactly ass'e'mbled relations-hip; said helical spr'ings also being aligned along said common horizontal. axis 'withthe turns of's'aid'first spring-coextensive with" a por tion of said heat coil, means forconnecting one element ofsaid spaced gap protector to said face plate, aterminalfor connection of arr-incoming line, a terminal for connection 30f a central 'ofiice" line, means including said. first helical spring fen-connecting the other-element of said spaced gap protector and one terminal of said heat coil to said incoming line terminal, and means including'said second helical spring for connecting the otherterminal of said heat coil to-said central offi'celine terminal.

2. An electrical protector comprising a.housing of insulating ma'te'rialj-a faceplate of'conduc-tive material for said'lious'ingj said housing-having a plurality "of recesses therein, a protector assembly "positioned'in'each' of the"recesses;'-'said "protector assembly including a' 'he'at coil and jaspaced gap protector, said spaced (gap roieewrwompn smg two cylindrical b'locksi and" means for holding said blocks in spaced relationship; saidjblocks and said "heat coil being aligned "horizontally in their respective recess" along 'a com-mon"*hori zontal axis,a "first and a second-helical'springfior exerting pressure on elements of said protector assembly, whereby to normally-maintaintl'idelments of the asse'r'nblyin compactly as'serrrloled relationship, said helical springs also" being aligned along said common horizontal axis with the turns of said first spring coextensive with a portion of'said heat coil, means" tor -connecting one element of said spacedgap protectorto-said face plate, an incoming line terminal, acen-tral oilice line terminal, means "including said first helical spring for connecting the othei -elernent of said spaced gap protector an'd 'o'ne'terminal of said heat coil to said inenm-ing' line terminal, means including said second helicalfspring for connecting" the "other terminal of sa'icl heat coil to said central ofiice line terminal, and means, effective upon removal of the'space'd gap no: tector elements of said protector assembly from the recess," for connecting the 7 incoming" "line directly to said Tace plate.

1 3.3 Anassembly of? protectors" of the J combined typerfor connection to ,a plurality of. electrical lines. cp'mpnsmg amusing" ,oflinsiilatienimaitfi i said :h'ousingl having awpluralityf of; spaced recesses therein rpassing from ,;tl 1e' f1; n1; surface to therrear snrfaceethereof af face-re ate for -said inousing'of conductive material ha. ,ing a plurality of apertures,Ithereinregisteimgresp 0'- ma with the recesses in .the' housing, a ro"-j tectorassembly-positioned in each of thereces'ses for,association-with the respective 1'nes;,eac of said: protector assemblies lcornpr g; an f op gap protector forI-iprotectionl again sneak'currents,.each of sja'id open gaprprotec ors comprising vtwo lcylindrical carbom blocksgand means forholdingwsaid lolockslin. spaced grelationship,,.said .open gap protector. and; said eatcoil being aligned horizontally m; their -r pectin; recess along a cornmonl oriz'ontal axisfia first ra-ndyasecondhelical; spring for exert ng pressure on" elements of a said protector assem ly whereby toflnormally lniaintain the .elern'entsf or the" as s'e fnbl y, in compactly assembled relationship; said helical Springs. also being aligned along, "id

common horizontal axis vwith the turns of i said first spring coextensive 'with a. portion of said heat c'oil, meansincluding said .firstl'spriri'g'for connecting an incoming-line tothefpro'te tb'r assembly, means including said se'condispriri'g f or connecting the. associated ofiice line tol tlie r0 teeter assembly, and means removablypositioiied in .the associated aperture 'in the face] platefo'r closing said aperture; said 'last-mentioned"means serving also a'sa housing for theinajor portion of said .open gap protector and as a means for electrically onnecting drieblock of 'saidopen'gap prote'c'toroto said faceplate. v W 4; An assembly of electrical ipmtectq sof the combined type for protectioniof a'pluralitypfindividual lines at a terminating point 'cpn'iprising a housing of jmol'dedplastic *insulation" material, said housing having a""plurality ofi dividual, spaced rece'sses therein 'passing 'fifom'tli'e front fa'ce of said'housing to theirear face tliereof -a race p1ate1oconductivematerialmounted onfth'e front 'face off'sai'd housing "having a plurality of iap'ertiires therjein'registering 'resp'ectivlywith "the recesses in saidihousing, removab1"meaiisfor normally closing saidtaperturea an" assembly of thefunctiona'l'protector elements-fora given line mounted in each of said recesses; -eacn oi -said functional protector element'asser'nblie's corn ising. an open' gap protector and a -h'eat aid opemgapprotectorcomprising-two carbonhlocl ts and means for holding said blocks 'in -spaced re lationship vvhereby to maintainagap'ofthe order off gmils betweenthetWo'fa'd-jacent facestl'iereof, said open gap protectorfandsaid-"heat coil being aligned horizontally in their respective recess alonga commonnonzontalfaxis; a fir'st' helical "spring and asecond helical spring" for exerting pressure on'elein'ents .of said protector assembly wherebyto normallyinaintain therelements o'f athe= assembly in compactly, -asse'rnbled;. relation-. 'shi-pg'r-said helical springs also being"; alignedalong saideommon horizontal axis with the turns 01; said first spring coextensive with a portion of said .heat coil means to electrically connect one :end of said first-spring toone of said carbon blocks and to one .tevrninal of said heat; .coil,-said-1:first spring having an extension arm thereon pnoject: ing fro'm'the rearcf sa'iclhous'ing, means forcone meeting" an incoming line directly tdcsaid extension .andn ie'ans for onnecting. tenements siazd carbon blocks to saidiace Npla'te said seco'iid 9 spring also having an extension arm thereon projecting from the rear of said housing, means to connect one end of said second spring to the other terminal of said heat coil, and means for connecting a terminating line directly to said extension arm of said second spring.

5. An assembly of electrical protectors of the combined type for protection of a plurality of individual lines at a terminating point comprising a housing of molded plastic insulation material, said housing having a plurality of individual, spaced recesses therein passing from the front face of said housing to the rear face thereof, a face plate of conductive material mounted on the front face of said housing having a plurality of apertures therein registering respectively with the recesses in said housing, removable means for normally closing said apertures, an assembly of the functional protector elements for a given line mounted in each of said recesses, each of said functional protector element assemblies comprising an open gap protector and a heat coil, said open gap protector comprising two carbon blocks and means for holding said blocks in spaced'relationship whereby to maintain a gap of the order of3 mils between the two adjacent faces thereof, said open gap protector and-said heat coil being aligned horizontally in their respective recess along a common horizontal axis, a first helical spring, means to electrically connect one end of said first spring to one of said carbon blocks and to one terminal of said heat coil, said first spring having an extension arm thereon projecting from the rear of said housing, means for connecting an incoming line directly to said extension arm, said removable closing means also serving as means for connecting the other of said carbon blocks to said face plate and as a housing for said other carbon block, a second helical spring, said second spring also having an extension arm thereon projecting from the rear of said housing, means to connect one end of said second spring to the other terminal of said heat coil, and means for connecting a terminating line directly to said extension arm of said second spring, said helical springs also being aligned along said common horizontal axis with the turns of said first spring coextensive with a portion of said heat coil, said springs serving to exert mechanical pressure against the protector assembly whereby to tend to move said assembly forward in said recess towards said face plate and against the restraining action of said removable closing means thereby normally maintaining the elements of the assembly in compactly assembled relationship.

6. An assembly of electrical protectors of the combined type for protection of a plurality of individual lines at a terminating point comprising a housing of molded plastic insulation material, said housing having a plurality of individual, spaced recesses therein passing from the front face of said housing to the rear face thereof, a face plate of conductive material mounted on the front face of said housing having a plurality of apertures therein registering respectively with the recesses in said housing, removable means for normally closing said apertures, an assembly of the functional protector elements for a given line mounted in each of said recesses, each of said functional protector element assemblies comprising an open gap protector and a heat coil, said open gap protector comprising two carbon blocks and means for holding said blocks in spaced relationship whereby to maintain a gap of the order of 3 mils between the two adjacent faces thereof,

said open gap protector and said heat coil being aligned horizontally in their respective recess along a common horizontal axis, a first helical spring and a second helical spring for exerting pressure on elements of said protector assembly whereby to normally maintain the elements of the assembly in compactly assembled relationship, said helical springs also being aligned along said common horizontal axis with the turns of said first spring coextensive with a portion of said heat coil, means to electrically connect one end of said first spring to one of said carbon blocks and to one terminal of said heat coil, said first spring having an extension arm thereon projecting from the rear of said housing, means for connecting an incoming line directly to said extension arm, and means for connecting the other of said carbon blocks to said face plate, said second spring also having an extension arm thereon projecting from the rear of said housing, means to connect one end of said second spring to the other terminal of saidheat coil, and means for connecting a terminating line directlyto said extension arm of said second spring, each of said extension arms having a biased lug thereon adapted to be seated in respective indentations provided in the'rear of said housing whereby to maintain said springs in assembled position.

"I. An assembly of electrical protectors of the combined type for protection of a plurality of lines at a central switching point comprising a housing of molded plastic insulation material, said housing having a plurality of individual, spaced recesses therein passing from the front face of said housing to the rear face thereof, a face plate of conductive material mounted on the front face of said housing having a plurality of apertures therein registering respectively with the recesses in said housing. removable means for normally closing said apertures, an assembly of the functional protector elements for a given line mounted in each of said recesses, each of said functional protector element assemblies comprising an open gap protector and a heat coil, said open gap protector comprising two cylindrical carbon block electrodes, means for holding said electrode blocks in spaced relationship whereby to maintain a gap of the order of 3 mils between the two adjacent faces thereof and means for providing an auxiliary gap between said electrodes in the form of a shallow circular recess surrounding the adjacent face of one electrode, said open gap protector and said heat coil being aligned horizontally in their respective recess along a common horizontal axis, a first and a second helical spring for exerting pressure on elements of said protector assembly whereby to normally maintain the elements of the assembly in compactly assembled relationship, said helical springs also being aligned along sa d common horizontal axis with the turns of said first spring coextensive with a portion of said heat coil, means including said first spring to connect an incoming line to one of said carbon block electrodes and to one side of said heat coil, means to connect the other of said carbon block electrodes to said face plate, and means including said second spring for connecting an associated terminating line to the other side of said heat coil.

8. A housing of insulating material, a face plate of conductive material for said housing, said housing having an aperture therein extending from the front face thereof to a point just short of the rear face thereof, a unitary protector assembly positioned in said aperture comprising a heat coilandfia' spacedgapiprotector', a shoul der in'saidaperture, aplurali'ty of'li'elical springs for holding. the-heat coil -andithe. spaced gapprotectorin. assembled positionwithinthe aperture, said facaplatehavinggan aperture therein-registeringwith .the fronti endllo-fltlie aperture in the housing said springsbeing. insertalole into the aperture. through the. face. plate aperture. and beingrestricted in theihmovement toward the rear of theaperturebycontact withv saidslfoulder and the rear. wall of" the aperture. respectively, removable means foriclosingzthe aperture in said faceplate, spaced aperturesthroughtl'ie rear wall of said first aperture... andlan extension arm on eacheof said springs, saidliextension arms passing through the apertures...in.saidirear wall and 'servingi both. as positioning. meansfor said. springs andasmeansior. electrically.v connecting external lines-thereto.

9. A- housing -.of ..insulation--material having. an open faced recess therein, a multielement protector. assembly; positioned in=tHe recess, .a plurality othelioalsprings positionedin. the recess and inser-talole therein through. the. open. face thereof, means includingtthe rear. wall ofth'e recess for restrictingthe movement-of saidsprings toward the rearottherecess, removable means .for closing the openiaceofLthe recess, said closingmeans when:- in .closing, position..bein effective. to bias the-protector assembly. towards the'rear. of the recess against the. yielding, restraint" of said springs and'to hol'd the assembly. in compact relati onshi-p with loothsprings in partially. compressed condition, therear Wall-of 'therecess having spacedapertures therethrou-gh, and extension arms on: said. springs, said. arms extending through theapertures and serving. both as positioning meansiorsaidlsprings.and as means for electrically. connecting. external circuits thereto.

10. An assembly oflelectrical protectors of the combined type.for protection of a plurality of individual .lines .at a terminatingv point compris- 12 mg" a? housing? of insulation: material; said 'hpuse ing: Having: a plurality" of individual; spacedwe' cesses therein; anassembiyrof the functional pro; tector elements for aJgiVeH line mountediii each" of said recesses, each of said} protector'e1ement' assemblies .coniprisin'g'a cap; an"open' gap; pro te'ctor including a pair of" spaced conductive blocks, and 'a lieatco'il', a:face"platepf'conductive material mounted on'the 'fr'ontifa'ce ofsaidhousing, means including a coiled spring forco'nnecting'an incominglirre" to-on'e side'of said heatcoil and one side" of said open. gap protector, .means The following references are of'recordfin the file of this patent:

UNITED STATESPATENTS.

Number v Name Date 8q5;i 54f Procunier Nov. 21'; 1904 1,974,257 Brandt Sept. 18', 1934 2,136,858 Michel Nov. 15, 1938 2,417,420 KiiapgJr: Mar; 1 8, 1947 FOREIGN PATENTS Nu'miier Country Date 353025: Netherlands e -Mar: 15; 1935 144,122? Switzerland: i n Mar; 2; 1931 

